1. Field of the Invention
The invention generally relates to wheelchairs, and more specifically to a method of wheelchair construction and resulting wheelchair.
2. Description of the Prior Art
There are two commonly used wheelchair design--the crossbrace folding wheelchair and the welded rigid frame wheelchair. The typical method of construction for both types of wheelchairs is to weld or braze metal tubes together to form frames and folding members. Unfortunately, the two above-described designs have one major flaw in common--the strength inconsistencies of the welded joints. Breakage of welded or brazed joints is the main cause for structural failure in wheelchairs. Welding or brazing also creates a heat-affected zone weakening the frame tube around the welded or brazed joints and making repairs in most cases impossible. Repairs and maintenance of these wheelchairs are costly and require elaborate service infrastructure. In addition, the welded construction makes it extremely difficult, if not impossible, to adapt the wheelchair to the end user's changing needs and environment. Conversion from rigid frame to a folding wheelchair is also virtually impossible.
It is desirable to have a wheelchair design constructed without welds or brazes. A weld-free wheelchair design would eliminate the shortcomings described above and open the door to endless new design possibilities.
Some wheelchair manufacturers build each of the wheelchair types listed above but they are of dedicated, welded construction and, for the aforementioned reasons, do not adapt from one type to another. There are chairs that are modular in design and can change the widths of the wheelchair with little difficulty. There is a design that converts from a user propelled to an assistant propelled wheelchair (U.S. Pat. No. 5,294,141). There is also a wheelchair that converts the riding position from the standard seating position to a recumbent position (U.S. Pat. No. 5,011,175). There is a weld-free folding wheelchair that folds in a non-conventional manner but is not modular (U.S. Pat. No. 4,682,783). Another wheelchair design appears to be a weld-free design that allows the wheelchair to adjust to different needs by use of special shaped bars and plates but is limited to width and depth adjustment (U.S. Pat. No. 5,743,545). There are several U.S. patents that claim to be modular, allowing for different components to be used to build the chair to the user's needs. Among these is a rigid frame wheelchair (U.S. Pat. No. 5,421,598), but again this wheelchair does not convert or adapt to the extent of this invention. There are several U.S. patents for wheelchairs that have welded or brazed construction.
In U.S. Pat. No. 5,253,888, issued to the assignee of the subject invention, a rigid frame weld-free wheelchair is disclosed that utilizes a series of special clamps for clamping tubes to each other. However, such weld-free construction has some disadvantages. A series of specially designed clamps had to be utilized which were not universal to all designs, making further design changes virtually impossible. Also, by virtue of the clamp designs, numerous bolts were required that were clearly visible and detracted from the appearance of the wheelchair.
There are no wheelchairs known to exist at this time that are constructed with distortion-free connectors and that can be configured or adapted to the extent of this design.